CODEWITHSUNDEEP
octave
user13549580
user13549580

Reputation:

Anonymous function using polynomial

Let's say I want to create a rational fraction function in GNU Octave. Can I do it easily using polynomial coefficients?

As example I would like to build

f = @(x) x.^2./(2*x^2+3*x+2)

using 

p1 = [1 0 0]
p2 = [2 3 2]

Upvotes: 1

Views: 281

Answers (2)

obchardon
obchardon

Reputation: 10792

You could also use the built-in function polyval:

p1 = [1 0 0]
p2 = [2 3 2]

f = @(x,p1,p2) polyval(p1,x)./polyval(p2,x)

Upvotes: 4

Ander Biguri
Ander Biguri

Reputation: 35525

With:

p1 = [1 0 0]
p2 = [2 3 2]

You can either do

f = @(x) sum([x.^2, x, 1].*p1) ./sum([x.^2, x, 1].*p2);

or

f = @(x,p1,p2) sum([x.^2, x, 1].*p1) ./sum([x.^2, x, 1].*p2);

I'd say the second one is clearer if you are going to be trying different polynomial coefficients.

if you want to have flexibility on the order of the polynomials, then you can even go further :

f = @(x,p1,p2) sum(x.^[length(p1):-1:0].*p1) ./sum(x.^[length(p2):-1:0].*p2);

Upvotes: 2

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